Production of phosphine



Nov. 5, 1963 D. T. PRlCE ETAL 3,109,737

PRODUCTION OF PHOSPI-IINE Filed July 27, 1960 3 Sheets-Sheet 1 E'PHOSPHORUS I 19 D. T. PRICE ETAL 3,109,787

PRODUCTION OF PHOSPHINE Filed July 27, 1960 3 Sheets-Sheet 2 CA E- PHOSPHORUS Nov. 5, 1963 D. T. PRICE ETAL PRODUCTION OF PHOSPHINE Filed July 27, 1960 5 Shets-Sheet s PHOSPHORUS CATHODE United States Patent 3,109,787 PRUDUCTION 0F PHGSPHINE Dennis Thornton Price, West Didsbury, Manchester, England, and Irving Gordon, Niagara Falls, N .Y., assignors to Hooker Chemical Corporation, Niagara Falls, N .Y., a corporation of New York Filed July 27, 1960, Ser. No. 45,567 8 Claims. (til. 204-101) This invention relates to the production of phosphine from elemental white phosphorus by an electrolytic process.

It is known that phosphine may be prepared by the action of alkalis on elemental phosphorus. However, the operating conditions of this reaction are difiicult and poor yields of phosphine, contaminated with large quantities of hydrogen and the lower hydrides are obtained.

It is also known that phosphine may be prepared by the reaction of water or acids on metallic phosphides. This reaction, however, is not economical since it produces many by-products, e.g. metallic oxides and hydroxides, which are not of any known value. In addition, the starting metal is usually expensive and red phosphorus must be used.

It is further known that phosphine may be prepared by thermal decomposition of the lower oxy-acids of phosphorus or their salts. This process is difficult to perform and poor yields of phosphine are obtained.

An electrolytic method of producing phosphine was noted by Grove in 1863. He passed an electric current through moist phosphorus and obtained phosphine (J. Chem. Soc. 16, 263 (1863)). The yield of phosphine in this case was poor as he attempted to pass an electric current through phosphorus itself, the high electrical resistance of the phosphorus thereby necessitating the application of a very high voltage. The only electrolyte present was the small amount of water in the moist phosphorus and this was inadequate to provide reasonable yield of phosphine.

A further possible method for the electrolytic production of phosphine is referred to by H. Blumenburg in United States patent specification 1,375,819. Blumem burg claims that when an electric current is passed through an aqueous electrolyte containing a compound of phosphorus e.g. phosphoric oxide or any salt of phosphorus, the nascent hydrogen produced at the cathode reacts in situ with the phosphorus compound to produce phosphine. Our experience is that this method, although it may be successful for the preparation of arsine, does not seem to work in the case of phosphine.

We have now found that phosphine can be prepared conveniently and in good yield by an electrolytic process for the direct reduction of elemental phosphorus in the molten state or in a finely divided state below the melting point, using for the cathode a metal having a hydrogen over-voltage and an aqueous electrolyte. in this process the metal cathode must continually or periodically come into contact with both the molten phosphorus and the electrolyte whilst the anode preferably comes into contact only with the electrolyte. Some suitable arrangement must be made to bring this into eflect. For instance, a pool of molten phosphorus on the cathode may be stirred or agitated by a motor driven or magnetic stirrer, or alternatively molten phosphorus may flow over an irregu- 'larly shaped cathode to achieve the same effect. Preferably the phosphorus is in a molten state.

According to the present invention there is provided a process for the production of phosphine by passing an electric current through an aqueous electrolyte between an anode and a cathode which is composed of a metal or metals having a hydrogen overvol-tage and which is 2 periodically or continually in contact with white phosphorus, the said white phosphorus being in the aqueous electrolyte bath but preferably never in contact with the anode.

Any material having a hydrogen overvoltage may be used for the cathode. Suitable metals which may be in a solid or liquid form include lead, mercury, zinc, copper, tin, cadmium, aluminium, bismuth, antimony, silver, palladium, iron, nickel, cobalt, chromium and alloys or combinations of these metals. When using a combination of cathode metals the minor component can conveniently be added as a soluble salt to the electrolyte from whence some or all of the metal is deposited upon the cathode. Mercury is a particularly useful cathode metal because of its high hydrogen overvoltage and also because its mobility assists in the stirring of the cathode-phosphorus interface to allow the electrolyte to reach the cathode.

When a vertical cathode is used a Wicking effect occurs between the cathode surface and the molten phosphorus, the phosphorus adhering to the surface of the cathode and rising above the phosphorus-electrolyte interface. This effect occurs in some instances before a. current is applied to the system, and in all cases after the current is applied. Agitation of the molten phosphorus enhances the effect. Molten phosphorus must be introduced into the cell to replenish that wicking up the cathode so that the lower end of the cathode is constantly in contact with molten phosphorus.

Any electrolyte which is non-reactive with molten phosphorus and which is capable of forming hydrogen ions under the electrolysis conditions employed may be used. Suitable electrolytes include aqueous solutions of phosphoric, sulphuric, hydrochloric or acetic acids and salts of these acids such as sodium, lithium or potassium chloride, sodium or potassium sulphate, and a monosodium or disodium phosphate. Mixtures of these electrolytes may also be used.

It has been found that the presence of certain metallic ions such as cadmium, zinc, lead, mercury, calcium, barium, bismuth and tin in the electrolyte gives an improved yield of phosphine.

Suitable materials for the anode will be obvious to those skilled in electrolysis e.g. platinum, lead, leadantimony, lead dioxide, graphite or stainless steel. When using a combination of electrolyte and anode which results in oxygen being evolved at the anode, loss of phosphine by oxidation in the solution may be avoided by the provision of a semi-permeable separator between the anode and cathode compartments. The use of a graphite anode which results in the production of carbon dioxide instead of oxygen at the anode avoids the need for proyiding such a separator.

Suitably the process is carried out using an electrolytic cell such as those shown in the attached drawings. I-n FIGURE 1 a glass vessel B is provided with an anode G and a cathode D, suitably a layer of mercury in the bottom of the vessel. A pool of molten phosphorus E lies on top of the mercury. The glass vessel B is provided with a mechanical stirrer C so that the mercury-phosphorus interface is kept in continuous agitation in order that the electrolyte can at least periodically come into contact with the cathode. At the cathode phosphine and hydrogen are produced and leave the cell through the cathode take-off A and the anode .gas leaves by the take oif H. The sintered glass disc F ensures that the phosphine does not pass into the anode compartment.

In FIGURE 2 a glass vessel B is provided with anodes G and a solid cathode D. A pool of molten phosphorus E is situated at the bottom of the cell and the cathode D dips into this phosphorus. At the cathode phosphine and hydrogen are produced and leave the cell through the gas take-oft A. The anode gas leaves the cell through the take-oil H. The diaphragrns F ensure that phosphine does not pass into the anode compartments. In FIGURE 3a glass vessel A is provided with a cathode compartment' B containing a fritted glass disc C which supports the liquid cathode D on which lies a pool of molten phosphorus E. The cathode lead wire I? is in a glass. tube which shieldsit from the other materials in the compartment. The compartment has a gas take oil G and an electrolyte level equalizer outlet H. An annular ring of a wire anode I is suspended below the level of the fritted glass disc C and positioned so that the ring diameter is entirely outside the outer edge of the cathode compaitment B. The anode lead wire I connected to the anode wire is shielded by a glass tube.

The phosphine produced by the above method may be used as starting material for the preparation of phosphonium compounds.

The following examples illustrate the production of phosphine by the electrolytic method.

Example 1 The following results were obtained using the apparatus shown in FIGURE 1 with a mercury cathode of weight 1-8 kg. having a surface area of 75 sq. cm. and a 1-2 molar orthophosphoric acid electrolyte. The cell was charged with 15 gm. of phosphorus.

Current Kwh. Rate of pro- Voltage density, Percent Percent per lb. duction of ma/cm. PH; Hz PHa phosphine,

' rug/hour Example 2 The following yields of phosphine were obtained using the apparatus shown in FIGURE 1 with a cathode consisting of mercury and mercury with other metals at a current density in the range 5.0 to 30.0 ma./cm.

Average percentage Cathode Electrolyte of phosphine in cathode gas Mereury+ zinc 4 molar orthophosphorie acid 79.0 Mercury bismuth 2 molar sulphuric acid 18.0 Mercury chromium do 60. 2 Mercury. do 63.0

Example 3 The following results were obtained using the apparatus shown in FIGURE 2 with a solid cathode at a current density in the range 8.0 to 30.0 ma./cm.

Example 4 As anexample of the wioking effect of phosphorus on a solid cathode, the apparatus of FIGURE 2, was used with porous lead peroxide anodes in glass anode compartments with the side toward the cathode faced with a semi-porous diaphragm, a sheet of commercial porous.

lead as cathode and a 40% solution of orthophosphoric acid as electrolyte. The phosphoric acid was introduced into the cell and the current turnedon to make the cathode cathodic. This reduced the oxides on the surface of the cathode. The cell was purged with nitrogen and 503 gms. of molten yellow phosphorus were added to cover the bottom of the cell and to be in contact with the bottom edge of the cathode sheet.

analysis gradually enriched in phosphine and after about 7 24 hours of operation reached a maximum value of phosphine at 2.9 volts and current density of 6.0 amps./ sq. ft. at about C.

Example 5 Using the apparatus of- FIGURES with a platinum wire anode, a mercury cathode, a 40% solution of phosphoric acid was introduced into the beaker A and the cathode compartment B to a level above that of the equalizer H and maintained at a temperature of 65 C. The cathode compartment B was purged with nitrogen, and enough commercial molten yellow phosphorus was added to cover the mercury surface.

When a voltage of 7.0 volts was impressed across the electrodes, 5.0 amps of current flowed giving a cathode current density of about 1 60 amps/sq. ft. Oxygen was generated at the platinum wire anode I and rose up external to the cathode compartment B. Within the cathode compartment B, it was observed that bubbles of phos phine and hydrogen were rising at the outer edge of and through the phosphorus layer. The cathode gas recovered was analysed with an alkaline NaOBr solution and contained 65% phosphine.

Example 6 contained in a porous ceramic tubular diaphragm and was adapted to vent oxygen gas from the anode, a thermometer, and a lead cathode sheet one inch lay three inches having a cathode lead wire and having a vent tube adapted to exit the phosphine and hydrogen gases from the cathode. When' the assembly was placed in the beaker, the bottom edge of the cathode was adapted to be near or in contact with the bottom of the beaker.

In starting up the cell, the current was turned on to make the cathode cathodic, this reduced oxides on the surface of the cathode. Next the cell was purged with nitrogen, and enough molten yellow phosphorus was added to cover the bottom of the cell, and to be in contact with the bottom edge of the vertical lead cathode.

Again the current was turned on, so that 0.5 ampere of electricity flowed at about 2.9 volts. Oxygen was produced at the anode, and phosphine began to be produced with hydrogen at the cathode. The phosphorus began to wick up. both sides of the cathode to the top. After an hour the surfaces of the cathode were totally covered with phosphorus. The temperature had increased to eighty-five degrees centigrade. The phosphine content of the cathode gas was determined by selective absorption Example 7 Using the cell and the electrolyte of Example 6, containing forty percent phosphoric acid and the lead salt, the platinum anode was changed to a lead anode. This caused the phosphine yield to increase to over eighty-five percent phosphine, atter three hours operation. After running overnight, it still was yielding eighty-seven percent phosphine.

Example 8 In a cell of duplicate construction with that of Example 6, a maximum of eight percent phosphine was produced even after running for eighteen hours at 0.5 ampere and about 4.0 volts, at temperature between sixty-three to seventy-two degrees centigrade. Lead acetate was then added and an increase of yield to twelve percent phosphine was noticed within a few minutes. At the end of six more hours operation, the yield had increased to fortyeight percent phosphine.

Example 9 In a cell of duplicate construction with that of Example 6, an electrolyte of forty percent phosphoric acid containing two cubic centimeters of :ten percent lead acetate solution was used. The cathode was covered with phosphorus after about six hours operation at 0.5 ampere and 2.5 volts, with the temperature varying from eighty-seven to ninety-five degrees centigrade. The phosphine yield increased from 17.5 percent to 25.5 percent phosphine in one hour. The cell was allowed to run overnight, and at the end of sixteen hours, was yielding 13.5 percent phosp-hine.

Two more cubic centimeters of ten percent lead acetate solution were added and alter five hours the cell was yieldring a forty-one percent phosphine cathode product. However, after ninety more minutes of operation, the yield had dropped to twenty-two percent phosphine. The cell was again run overnight and alter eighteen hours was producing a cathode product of twenty-four to twenty-six percent phosphine. More lead acetate solution (eight ccs.) was added, and within two hours the cathode gas product had increased to fifty-four percent phosphine. The cell was again allowed to run overnight and after twentyone hours was producing a cathode gas containing fortyfive percent phosphine.

Example 10 In a cell of duplicate construction with that of Example 6, an electrolyte of forty percent phosphoric acid was used. A cathode gas product was recovered analyzing 8.5 percent phosphine. The cell Was operated at temperatures from seventy-one to seventy-four degrees centigrade, and at from between 3.5 and 3.9 volts with a current flow of from between 0.2. and 0.8 ampere. Then four cubic centimeters of ten percent barium chloride solution were added to the electrolyte. After one hour the cathode product yield had increased to fourteen percent phosphine, and after live more hours the yield had increased to twentythree percent phosphine. The cell was allowed to run overnight and after seventeen hours, the yield of phosphine was still twenty-one percent.

Example 11 To the cell of Example 10, containing forty percent phosphoric acid and four ccs. of ten percent barium chloride solution were added four ccs. of ten percent cadmium phosphate solution. After ninety minutes the cathode product yield had increased to forty-one percent phosphine, and alter five more hours the yield had increased to fifty-six percent phosphine.

Example 12 In a cell of duplicate construction with that of Example 6, an electrolyte of forty percent phosphoric acid was used. The cell was operated at eighty degrees centigrade, and 3.6 volts with 0.5 ampere of current and gave a cathode product yield of 5.5 percent phosphine. Four ccs. of ten percent zinc chloride solution were added, and after an hour the cathode product yield had increased to eleven percent phosphine.

Example 13 In a cell of duplicate construction with that of Example 6, an electrolyte of forty percent phosphoric acid was used. The :cell was operated at eighty degrees centigr-ade and 3.9 volts, with a current flow of 0.5 ampere to give a cathode product yield of 7.5 percent phosphine. Four cubic centimeters of ten percent calcium phosphate solution were added and after twenty-five hours the cathode product yield had increased to 25.9 percent phosphine.

Example 14 In a cell of duplicate construction with that of Exampie 6, except that a one inch by three inch cathode of Mumetal (which is an alloy of 77.2 percent nickel, 4.8 percent copper, 1.5 percent chromium and 14.9 percent iron), an electrolyte of forty percent phosphoric acid was used. The cell was operated at about ninety-five degrees centigrade, and 2.5 volts with 0.5 ampere of current. No phosphine was produced. Four cubic centimeters of ten percent lead acetate were then added. The phosphine yield increased to fifty-five percent PH in one hour. After 4.5 hours the cell was still yielding a cathode product of fiftynine percent PH The cell was run overnight and after sixteen more hours was producing a cathode product of eighty-five percent PH Example 15 Using the cell of Example 6 with a cathode of a tin-bismuth alloy (one inch by three inches by one-eighth of an inch), and an anode of tin-bismuth alloy, an electrolyte of forty percent phosphoric acid was added to the cell. Twenty grams of elemental white phosphorus were placed in the cathode compartment. The temperature of the cell was maintained at eighty degrees centigrade, and a direct current of 0.5 ampere was maintained at approximately 3.4 volts. After about twenty-four hours of operation, the tin-bismuth alloy anode was removed and replaced with a platinum wire anode. The phosphine concentration in the cathode gas under these conditions increased from nine percent to 15.5 percent after six hours, and then decreased to six percent in two hours. After an additional nineteen hours, during which the phosphine concentration was six percent, the platinum anode was replaced with the tin-bismuth alloy anode. After 4.5 hours of operation, the alloy was replaced With the platinum anode. Sixteen hours after inserting the platium anode, the cathode gas contained ninety-five percent phosphine by volume. Atter five days of operation under these conditions, during which time the phosphi-ne concentration was greater than about ninety-two percent phosphine, the phosphine concentration decreased to about seventy percent :due to depletion of molten phosphorus in the cathode section. After addition of phosphorus to the cathode section, the phosphine concentration in the cathode gas was greater than about ninety-two percent by volume for two additional days. The concentration then fluctuated in the seventy to eighty percent range for eighteen additional days. For the next sixteen days the cathode gas contained about fifty percent phosphine by volume.

We claim:

1. The process for preparing phosphine which comprises contacting an anode and a cathode with an aqueous electrolyte, at least a portion of the cathodic surface or said cathode contacting elemental phosphorus, and maintainling an electric current between said anode and said cathode through said electrolyte, whereby a phosphine-containing gas is produced at the cathode.

. 2. The process for preparing phosphine which cornprises contacting an anode and a cathode with an aqueous electrolyte, contacting a portion of said cathode with molten phosphorus, and maintaining an electric current between said anode and said cathode through said electrolyte, whereby a phosphine-containing gas is produced at the cathode.

3. The process for preparing phosphine which cornprises contacting an anode and a cathode with an aqueous electrolyte, contacting a portion of said cathode With molten phosphorus while maintaining said anode free from contact with said molten phosphorus, and passing an electric current between said anode and said cathode through .said electrolyte, whereby a phosphine-containin-g gas is 7; The process of claim 1 wherein said electrolyte is an aqueous solution of phosphoric acid.

8. A process for preparing phosphine which comprises contacting an anode and a cathode with an aqueous electrolyte, at least a portion of the cathode surface of said cathode containing elemental phosphorus, and maintaining an electric current between said anode and said cathode through said electrolyte, whereby pho-sphine is produced at the cathode.

References Cited in the file of this patent UNITED STATES PATENTS 362,257 Dudley May 3, 1887 1,375,819 Blumenber g Apr. 26, 1921 1,970,973 Palrnaer Aug. 21, 1934 2,867,568 Cunningham 1 Jan. 6, 1957 2,913,383 Topfer Nov. 17, 1959 FOREIGN PATENTS 6,007 Great Britain July 16, 1892 1,130,548 France Oct. 1, 1956 OTHER REFERENCES Pauling: College Chemistry, 1955, pages 330-5.

Ephraim: Inorganic Chemistry, 5th Edit-ion, 1948, pages 617-22.

Treatise on Powder Metallurgy, by Goetzel, volume III, 1952, page 63 (#907).

Journal of the Chemical Society, volume 16, 1863, pages 263-72. 

1. THE PROCESS FOR PREPARING PHOSPHINE WHICH COMPRISES CONTACTING AN ANODE AND A CATHODE WITH AN AQUEOUS ELECTROLYTE, AT LEAST A PORTION OF THE CATHODIC SURFACE OF SAID CATHODE CONTACTING ELEMENTAL PHOSPHORUS, AND MAINTAINING AN ELECTRIC CURRENT BETWEEN SAID ANODE AND SAID CATHODE THROUGH SAID ELECTROLYTE, WHEREBY A PHOSPHINE-CONTAINING GAS IS PRODUCED AT THE CATHODE. 